by Steve J » Tue Dec 20, 2016 9:16 pm
Without removing the head, you will only be able to tell whether it's a small block or large block engine casting. You could try measuring the separation between cylinder head studs, and comparing your measurements with a couple of spare 150 small block and 200 large block head gaskets. Dropping the exhaust and measure the width of the exhaust port may give a clue - you may even be able to measure the bore (approximately). Remove the inlet manifold and measure the separation between mounting holes - small block and large block cylinders are different, but it's not conclusive. (It's been known for 200 Lambro 3-wheeler barrels to be fitted to large block engine castings, but those have the same inlet manifold stud spacing as the smaller cylinders.) The small and large block castings are different around the transfer port areas, but not that easy to see when the engine's installed. I'd be inclined to remove the head and do a direct measurement - head gaskets are cheap enough.
Even if you measure the bore, and get a reading of 66mm, it could still be a small block engine with overbored cylinder.... or one fitted with a remachined 200 cylinder. Maybe posting a few photos would be a good idea.
For what it's worth, I've got an Indian 150 engine casing, the prefix is S401 on that - anyone got one with a S602 prefix?